1. Field of the Invention
The present invention relates to a method for detecting touch and an apparatus for detecting touch using the same.
2. Discussion of Related Art
As detection methods currently used in touch screens, a resistance film method, a surface ultrasound method, and a capacitance method are mainly used, and the capacitance method makes multi-touch detection possible and has excellent durability, visibility, and the like, and therefore there is a trend of adapting the capacitance method as a main input means of portable mobile devices.
A touch screen of the capacitance method recognizes a user input by detecting changes in an electric charge amount that is charged into capacitive sensors on a touch screen panel by user interference, and is classified as a self-capacitive touch screen or a mutual-capacitive touch screen in accordance with an electric charge storage method. The self-capacitive touch screen includes a single conductor for each capacitive sensor so as to form a charged surface with a reference ground outside the touch screen panel, whereas the mutual-capacitive touch screen enables two electric conductors on the touch screen panel to mutually form a charged surface so as to function as a single capacitive sensor.
A general self-capacitive touch screen uses an X/Y orthogonal type conductor arrangement, and in this case, each capacitive sensor functions as a line sensor, and therefore only one piece each of X-detection information and Y-detection information is provided from each of an X-line sensor group and a Y-line sensor group when detecting the touch screen. Therefore, the general self-capacitive touch screen makes detection and tracking of a single touch possible, but cannot support a multi-touch. The mutual-capacitive touch screen also uses an X/Y orthogonal type conductor arrangement but each capacitive sensor is configured in the form of a grid sensor for each position orthogonal to the conductor. The mutual-capacitive touch screen is different from the self-capacitive touch screen in that reactions of all grid sensors are independently detected when detecting a user input on the touch screen. Each grid sensor corresponds to one pair of X/Y coordinates and provides mutually independent reaction results, and therefore, in a mutual-charged touch screen, a multi-touch of a user may be detected and tracked by extracting user input information from an X/Y-detection information set provided from a set of X/Y grid sensors.
A configuration of a conductor of a general mutual-capacitive touch screen panel and a detection method thereof are as follows. First electrodes including conductors extending in any one direction and second electrodes including conductors extending in a direction orthogonal to the first electrodes form a mutual-capacitive sensor by a dielectric material between the two electrodes. A capacitance C of the mutual-capacitive sensor is defined as C=∈*a/d when a distance between two electrodes is “d,” an area of a charged surface is “a,” and an equivalent dielectric constant of all dielectric materials between the charged surfaces is “∈,” and has a relationship of Q=CV with an electric charge amount Q charged into the sensor and a potential difference (voltage) V applied to two electrodes/charged surfaces. When a user approaches the sensor, interference with respect to an electric field formed between the two electrodes occurs to prevent electric charge from being stored in the sensor, and therefore an electric charge amount charged into the sensor is reduced resulting in a reduction in capacitance. This may be understood as being caused by changes in the capacitance due to changes in the equivalent dielectric constant between the charged surfaces by the user's approach, but a reduction in electric charge amount/storage amount due to a part of the electric field between the charged surfaces being shunted by the user's approach is an actual physical phenomenon. When an AC voltage source is connected to the first electrode to apply an AC waveform to one charged surface of the sensor, variation (ΔQ) in the charge amount corresponding to ΔQ=CΔV with respect to C which varies in accordance with a degree of the user's approach occurs, and a read-out circuit connected to the second electrode converts the variation into a current or a voltage. Such converted information is generally subjected to signal processing operations such as noise filtering, demodulation, digital conversion, accumulation, and the like to be used in a coordinate tracking algorithm and a gesture recognition algorithm. As a prior patent concerning such a capacitive touch-sensitive panel, U.S. Pat. No. 7,920,129 is disclosed.
A signal source applies electric signals to a driving electrode of a touch panel so that an object shunts an electric field flux formed in the driving electrode and a sensing electrode, and a change in a current occurs in the sensing electrode in accordance with a change in the electric field flux due to the shunt. A signal conversion unit connected to the sensing electrode detects the change in the current to determine presence/absence of touch by the object. When noise flows into the current which is required to be detected in order to detect the touch, it may affect information detection such as touch coordinates and the like, resulting in occurrence of an error in information such as detected coordinates and the like.
Various kinds of noises flow into the touch panel. As an example, when an LCD display is disposed below the touch panel, LCD noise due to a Vcom voltage of the LCD may affect the touch panel. Noise radiated from the LCD display may be prevented from flowing into the touch panel by connecting the remaining driving electrodes other than the driving electrode to which electric signals are applied to a low impedance source to form the electric field flux among the driving electrodes formed in the touch panel. In addition, various kinds of noises flow through an object that applies a touch input, and the noises flowing through the object are radiated from a large number of noise sources such as fluorescent lights, lighting equipments and the like and collected by human bodies to be applied to a panel. Noise radiated from a common electrode of the above-described LCD is shielded by the driving electrodes to minimize effects of the noise, but noise flowing through the object cannot be shielded.
In addition, noise having a large frequency difference with signals which are applied in order to drive the touch panel may be removed by performing filtering on the noise, but noise having the same frequency as or an adjacent frequency to the signals which are applied in order to drive the touch panel cannot be removed by performing the filtering on the noise.
In the related arts, touch coordinates are obtained by driving the touch panel using three mutually different signals having three discrete frequencies which are arbitrarily extracted, the obtained touch coordinates are arithmetically operated by performing median filtering in which an intermediate value is used by discarding a maximum value and a minimum value of the obtained result, majority selection filtering in which a result exhibited most frequently in the obtained touch coordinates is used, average selection filtering in which an average value from the obtained result is used, or the like is performed, and then further processing is performed. However, in such related arts, signal processing should be performed by the number of selected frequencies, and therefore power consumption is increased in the signal processing several times, and a time required for obtaining the touch coordinates is increased.